DNA Sequence Requirements for the Activation of 434 P RM Transcription by 434 Repressor

Abstract

A dimer of the 434 repressor bound at O_R2 activated transcription initiation from P_RM by contacting RNA polymerase. Although DNA-binding site mutations at either end of O_R2 decreased the ability of the repressor to activate P_RM transcription, mutations proximal to the promoter had a greater effect on transcription activation. Orienting a repressor subunit bearing the altered specificity Gln-28 → Ala mutation to the halfsite of O_R2 proximal to the P_RM promoter decreased the repressor's ability to activate transcription initiation at 434 P_RM to a much greater extent than if this subunit was placed in the O_R2 half-site distal to P_RM. In addition to showing that the downstream (promoter proximal) subunit of the O_R2-bound 434 repressor functions in activating 434 P_RM, the results indicated that DNA sequence-dependent conformational changes alter the efficiency with which the repressor activates P_RM transcription. These unexpected findings highlight the importance of the structure of the repressor-DNA interface in activating transcription from P_RM.